1. Field of the Invention
The present invention relates to an olefin polymerization catalyst. More particularly, the present invention relates to an olefin polymerization catalyst which exhibits high activity on its application to the polymerization of olefins and makes it possible to produce a polymer having high stereoregularity and a large particle diameter.
2. Description of the Prior Art
Hitherto proposed olefin polymerization catalysts comprising a solid catalyst component containing titanium, magnesium and a halogen as the essential components and an organoaluminum compound exhibit high activities and high stereoregularities. However, polymers obtained through their use generally have unsatisfactory average particle diameter and thus are required to be subjected to granulation process in the final step of the polymerization process. The elimination of the granulation process should drastically improve the production efficiency and thus successfully decrease the production cost.
In the polymerization without the use of a solvent, the increment of the polymerization amount of a rubber component primarily comprising a propylene-ethylene copolymer during the production of a propylene block copolymer by stepwise polymerization including the copolymerization with a small amount of ethylene often gives rise to deterioration of fluidity due to the adhesion of polymer particles and causes a very serious operational problem. The problem is believed to be mitigated by sufficiently increasing the particle diameter of the polymer particles. The overcoming of this problem indicates that a block copolymer having a high content of a rubber copolymer, the production of which the production has hitherto been considered very difficult or almost impossible, can be readily produced. Thus, it is desirable to develop a series of highly active and highly stereoregular catalysts which afford polymer particles having a sufficient particle diameter for accomplishing the above described object.
It is believed that a catalyst having a particle diameter corresponding to a granular polymer having a large particle diameter is required for the production of the granular polymer. In the case of a catalyst having a magnesium compound and a titanium compound as the essential components, a method of first preparing magnesium containing particles having satisfactorily large particle diameters is known as one of the aforementioned concept. For instance, Japanese Patent Publication No. 45643/1986 discloses a method of granulation by melting a dihalogenated magnesium compound and spraying it into a desired particle state. Japanese Patent Laid-Open Publication No. 29591/1980 discloses a method of obtaining the desired particle state by forming an emulsion of a melt comprising a dihalogenated magnesium and an alcohol together with an inert medium and cooling it into a solid.
The aformentioned proposals however require large expenditures for equipment and produce a catalyst having a low activity per catalyst containing magnesium containing particles which have satisfactorily large diameters. Thus these proposals are considered to still have points to be improved. As an alternative method, the method for preparing a catalyst having a desired particle diameter by separately providing particles other then dihalogenated magnesium containing particles for a support having a sufficient diameter and supporting a catalyst on the particles is described in Japanese Patent Laid-Open Publication Nos. 98604/1989 or 97508/1990 and in U.S. Pat. No. 4,940,682. These catalysts, however, have unsatisfactory activity per catalyst containing the support particles, or may cause problems such as fish-eye during molding since the support particles are particles of a divinylbenzene-styrene copolymer which may be crosslinked.
The present invention seeks to solve problems such as those encountered in the prior art.